HP 12C - 12c Platinum -- VAT amount, NET, GROSS

[Dr_Who2]

Hello everyone,

I am new to this forum and here comes a warm greeting to all members.

As for my person, I am no mathematician nor an engineer.
If I have to do any calculation in the field, it is related to financial problems or tasks.

To make a long story short, I obtained a new HP-12C Platinum mostly for nostalgic reasons and since I was curious about the so called RPN method.
As luck would have it, I also received in addition a pre-owned HP-12C as a gift.

Now, recently I had to calculate net and VAT-amount from gross amount given to me in a hand written list. Knowing the tax rate (19%), I thought this to be an easy out of the box task.
I soon figured, it is not.

The underlying math is no problem.
Since I received a quiet long list, I wished the HP-12CP and HP 12-C respectively had a key to deduct and/or add the tax instantly.

I found this entry in the old archive Forum: Posted by Kalevipoeg on 26 Nov 2005

This helped a lot.
While the approach from Kalevipoeg helps to deduct the tax, it naturally does not work vice versa. The approach is nice, since once the program is keyed in, it takes few key strokes to get the desired result.

I found the Message #3 by tony(nz) in the above thread most helpful, since it works both ways.
This is to say, if i, n (1) and PMT (0) are given, you can either enter the net amount (PV) or the gross amount (FV).

The approach from Tony really solved the problem at hand with the HP-12CP.
The procedure goes as follows:

0 -> PMT
1 -> n
19 -> i
238 -> FV
Press PV for net amount
= -200

This also works vice versa

0 -> PMT
1 -> n
19 -> i
-200 -> PV
Press FV for gross amount
= 238

Now, with this you get either the net value or the gross value. If one has a long list with gross values, you simply once key in n, i and PMT and you are ready to go as long as you wish.
What you miss, is probably the VAT amount.

On the HP-12CP this is simply done by pressing the + key right after.
This will not alter the given i, n, and PMT values.

Now, having figured this out, I thought to use the same method on the HP-12C.
The advice by Tony works as well here, but pressing the "+" key at the end is where this version differs.

I tried several times with both devices only to figure, that the HP-12C does work differently.

I investigated and I think, this comes down to where the given numbers and results are stored in each device.

The HP 12CP stores given financial values and the calculated result also in the stack.
e.g. if you give

0 -> PMT
1 -> n
19 -> i
238 -> FV
Press PV for net amount
= -200

If I look up the stack content after pressing PV on the HP-12CP with the R key, there is the following content
x = -200
Y = 238
Z = 38
T = 19

Press + for VAT amount = 38

If I look up the stack content on the HP-12CP with the R key now, there is the following content:
x = 38.00
Y = 19.00
Z = 1.00
T = 1.00

Now for the HP-12C:

If I look up the stack content after pressing PV on the HP-12C with the R key, there is the following content
x = -200
Y = 0.00
Z = 19.00
T = 19.00

Press + for VAT amount and the stack shows as follows:
x = -200.00
Y = 19.00
Z = 19.00
T = 19.00

This may be well known to the educated members and specialists on this board.

I just thought, this entry might add to the above mentioned thread by Kalevipoeg or the solution by Tony and avoid confusion for others.

Hope this helps someone and thank you Kalevipoeg and Tony for the provided help long time ago.

In case of any interest:

My HP-12CP was made in Phillippines, 2 batteries and on the front side, lower left, there is no "Hewlett . Packard" written, but plain the outer, continues line in silver. A sticker for serial #.

My pre-owned HP-12C was made in Malaysia, 3 batteries and has a stamped Serial #.

None of them has a securing screw on the battery lid.

[2old2randr]

Interesting.

I tried the same thing but I get different results on an HP 12c+ (the one with 2 CR2032 batteries).

I did 1 ENTER, 2 ENTER, 3 ENTER, 4 to fill the stack (T=1, Z=2, Y=3, X=4). Then 0 PMT 1 n 19 i 238 FV PV. Now when I look at the stack, I find T=2, Z=3, Y=4 and X=-200.

In other words, the stack is not disturbed except to display the final result. The original, X, Y and Z values are preserved.

[AndiGer]

The Enter key mustn‘t be pressed before entering into TVM values.
Just the sequence: value - TVM key - value - TVM key …
Enter is only needed to separate values and copy x to y.
Andi

[Dr_Who2]

thx 2old2randr and AndiGer for the reply.

@ 2old2randr:
Thx for taking your time to participate.
Just to avoid any confusion:

I. My HP-12CP
1.
With my HP-12CP off, if I press and hold "g" and "Enter" and then "ON", then release ON, then "g" and then the "Enter" key, right in that order, I receive the following on the display:

1.L 2.C 3.H 4.CPU

[I guess, what I read as "H" is supposed to be a "K", because hitting 3 enables a test of all keys with every digit on the display lit and going partially off, as I press every key]

However, pressing 2 reveals
ChE - - 564Ah

pressing "Enter reveals
VEr 02

pressing "Enter" again reveals
C 2004 hP

pressing "Enter" the last time, reveals the initial start ( 1.L 2.C 3. H 4.CPU )

pressing "4" reveals
3939790 h2

Not much more, I can say about this device.

2.
Removing the battery lid on this HP-12CP , there are 2 CR2032 batteries. Between them and slightly above their compartment, there is a square hole internally covered with a black plastic strip; probably covering an interface for ROM updates. I will not remove that to find out as of now.

II.
@2old2randr: What happens if you press "+" right after PV? By the stack content you gave, my guess is, it calculates -196 ( -200 + 4 = ) since 4 is saved in Y-Stack in your model, as you described.

III. HP -12CP doing math
I checked with my HP-12CP again using your description and in that order.
My results, regarding the individual stack content, remains the same as before.

1.
Just to be sure, I checked after each TVM keypress the content of the x,y,z,t stacks:

So, following 1,2,3, each separated with "Enter" and finally pressing 4,
stack wise I can see the following:
t: 1
z: 2
y: 3
x: 4

Now keying in "0 PMT" results in
t: 2
z: 3
y: 4
x: 0

Then keying in "1 n" results in
t: 3
z: 4
y: 0
x: 1

Then keying in "19 i" results in
t: 4
z: 0
y: 1
x: 19

Then keying in "238 FV" results in
t: 0
z: 1
y: 19
x: 238

Now, if I press "PV", I get the following result
t: 1 (n value)
z: 19 (i value)
y: 238 (FV value)
x: -200 (calculated PV result)

2.
Note: From what I estimate, every hit on one of the TVM keys stores that information in its according financial memory and at the same time, elevates the x-Stack, as if you have hit "Enter", hence the given value is elevated to the y-stack and so forth.

For this pressing "+" right after PV, results in ( x + Y = | -200 + 238 = ) 38

III. HP-12C (3 Batteries) same calculation
Now, I did the same procedure with the HP-12C.

a) 1,2,3, each followed by ENTER and keying 4 as last key shows the stacks content as described. No worries here.
b) 0 PMT, 1 n, 19 i shows also no difference to the HP-12CP stack content
c) 238 FV and stacks are still as expected
d) pressing "PV" shows a difference, the stack content reads
t: 0 (PMT value)
z: 1 (n value)
y: 19 (i value)
x: -200 (calculated PV result)

To me, it looks like on this model/ROM-version, pressing PV

1. does store to the financial memory and is to the x-stack while
2. pressing PV will not elevate the former FV value to y-stack and
3. overwrites the x-stack (former FV value) with the calculated PV value.

For this, pressing "+" will not give you the VAT amount as the HP-12CP does.

@ AndiGer
Thank you for the comment. I guess, 2old2randr tried to figure out the stack content, hence filled them up with values, so just to check. I read his description regarding keying in TVM values as you indicated, so without "Enter".

IV.
@ all
Over all, I think this is an important difference between the two devices I have.
Even more, if one wants to program something, that relies on TVM/stack-content.

Since I am currently not aware, what other financial calculations and keys behave differently between the HP-12C and HP-12CP, older programs for the HP-12C might not be suitable or flawed for the HP-12CP and vice versa.

Kalevipoeds program is not affected, since he does not rely on the TVM keys and what stack is filled with what pre given value. Tony´s approach lesser so, even though for the HP-12CP it works just as fine and requiers no self written program.

It might sound questionable to pursue this issue, but since both devices have CFP® and CFA® Certification Exams, GARPFRM™ Exam, some people might look up solving common, financial tasks like the given, fairly small problem.
They might end up unsatisfied with the usability of the device, if a given or suggested solution does not work for them on their device.

Looking at the HP-12C, it would have not been a bad idea by HP (40 or so years ago), to implement ("g" +) as add Tax and ("g" -) as deduct Tax to ease this common task.
For the HP 12CP it could have been ("f" STO) to add tax and ("f" RCL) to deduct tax.

kind regards

[BruceH]

(04-27-2023 12:05 PM)Dr_Who2 Wrote:  Now, recently I had to calculate net and VAT-amount from gross amount given to me in a hand written list. Knowing the tax rate (19%), I thought this to be an easy out of the box task.
I soon figured, it is not.

One of the best features of the 12C is that it is ideal for short and sweet programs and this is a perfect example.

Assuming the formula \(net = gross / 1.19\) and \(vat = gross - net\) then this is easily done on the keyboard using the keystrokes:

123.45 ENTER ENTER 1.19 ÷ "display now shows net amount" − "display now shows vat amount"

This is fine but having to type 1.19 repeatedly is tedious so turn it into a short program:

Code:

[f][PRGM] to erase any existing program
[f][P/R] to start recording a program
[ENTER] [ENTER] 1.19 [÷] [R/S] [−] [R/S]
[f][P/R] to stop recording the program

Now all you have to do is enter the gross amount and press [R/S] to see the vat amount, then press [R/S] a second time to see the net amount.

Repeat with the next amount until done. No need to press ENTER after each amount as it's in the program - the [R/S] does it all.

[2old2randr]

(04-28-2023 02:33 PM)Dr_Who2 Wrote:  @2old2randr: What happens if you press "+" right after PV? By the stack content you gave, my guess is, it calculates -196 ( -200 + 4 = ) since 4 is saved in Y-Stack in your model, as you described.

Yes, correct. Pressing '+' displays -196 as expected.

My HP 12c is the recent model (much faster than the original 12c or the 12c Platinum). The copyright info reads - ChE -- A3A3h, 2009-07-02, C 2008 hP.

I thought the ROM on this model was identical to the original 12c but it is evidently not so given the different results on your Malaysia model. Thinking about it, I prefer the behavior on my 12c since I don't expect the stack to be changed when using the financial registers.

[Gamo]

Even better if no need to manually key in or use program to find VAT Exclusive.

If one need to to find VAT Exclusive often the TVM function can be use to do this type of problem.

My example usage will use 7% VAT Rate

Example:

This item price is 2354 VAT included. Find price not include VAT

Set Up:

Always put 1 to [n] and this case VAT Rate is 7% put 7 to [i]

[PV] is for Price not include VAT
[FV] is for Price include VAT

Put 2354 to [FV] then press [PV] to find Price not include VAT is -2200

Just ignore the negative sign convention and answer is 2200

The same data still intact if price not include VAT is 1100 What is the price include VAT

1100 [PV] [FV] display answer and ignore negative sign is 1177

Remark:

To find VAT Amount simply press [RCL] [FV] [RCL] [PV] [+]


Gamo 4/29/2023

[Dr_Who2]

I really appreciate the given thoughts and observations. Thank you all for the feedback, hints and advice.

I learned, that not every HP-12C variant is the same regarding what is when saved into the stack.
The TVM memory seems to remain untouched on both devices.
Meanwhile, I can see at least three reliable methods, that work on either of the devices:

1. The one given by BruceH through a short program (see below),
2. the one by Khalevipoeg through another short program with the results saved in the x and Y stack [remeber to use the [R scroll key].
3. the one by Gamo utilizing the given TVM keys and utilizing [RCL] key.

@2old2rndr:
Indeed, interesting difference. Since I needed the VAT amount, your calculator does not provide that through TVM by pressing the [+] at the end, while my HP-12CP does.
For other calculations, it might be more useful to not have the TVM values written into the stack, while doing TVM calculations at the same time.

@BruceH
I tried that little program. Works fine on both devices.
However, and this is no big issue, but regarding this statement

"Repeat with the next amount until done."

The second time you give the amount (inkl. VAT) and press R/S, it will not start right away.
One has to press R/S on my devices an additional time first, to start the programed calculation.
After that, it works as described.
I tried putting [g] [GTO] [00] at the end of that little program at no avail.
Still needs an extra [R/S] to start, when the second, third, etc.. value is given.
I am not sure why that is.
Ultimately, it does work though and spares repetitive entry of the VAT % value.

@Gamo
Thank you for reminding about [RCL] while doing TVM calculations. Since I am new to this, I payed no attention to this key. This method works on both calculators and gives the VAT amount.
When I gave [FV] first and press [PV], I get the net value [excluding VAT].
However, right after, pressing [RCL] [FV] [+], gives the VAT amount.
There was no need to use [RCL] FV [RCL] PV [+] to get the result, as [RCL] "first given value" is enough, to get the VAT amount.
Maybe, this is what you meant, as you indicated about both calculations.

Again, thank you all for support.

[BruceH]

(05-02-2023 10:34 AM)Dr_Who2 Wrote:  @BruceH
I tried that little program. Works fine on both devices.
However, and this is no big issue, but regarding this statement

"Repeat with the next amount until done."

The second time you give the amount (inkl. VAT) and press R/S, it will not start right away.
One has to press R/S on my devices an additional time first, to start the programed calculation.
After that, it works as described.
I tried putting [g] [GTO] [00] at the end of that little program at no avail.
Still needs an extra [R/S] to start, when the second, third, etc.. value is given.
I am not sure why that is.
Ultimately, it does work though and spares repetitive entry of the VAT % value.

D'oh. Sorry - you can fix it by getting rid of the last [R/S]* so

Code:

[f][PRGM] to erase any existing program
[f][P/R] to start recording a program
[ENTER] [ENTER] 1.19 [÷] [R/S] [−]
[f][P/R] to stop recording the program

* I had an earlier version with [R/S] to pause the output then GTO 0 to go back to the start but realised it wasn't necessary... removed the GTO and forgot the [R/S].

[Dr_Who2]

@BruceH
Lovely and thank you for clarifying and it is easy to memorize.
Works now like a charm.

@all
Just figured, US seller give prices without sales tax.
Latter one is added when you pay/check out. This explains the unshiftet [%] key.

Not so in Europe, where sales tax for consumer is always included in the given price.

Reminding me of this indicates, why HP, an US company, provides no direct solution for my rather simple task in the handbook. In the US, it was not necessary to deduct sales tax.

I am happy for every hint and solution I got through this thread.
It deepened my knowledge about basic RPN, dedicated memory, stacks and programing a voyager series financial calculator.

Highly appreciated

[goosnarrggh]

I recreated the test proposed by 2old2randr.
1. Set the stack's initial state with recognizable values 1 2 3 4.
2. Then, key in some financial data without pressing ENTER: n=1, i=19, PMT=0, FV=238.
3. Finally, compute PV.

From my sample, I'd say that all the 12C's in my possession have identical behaviour:
- 3-SR44-cell genuine Nut CPU, manufactured in Singapore
- 1-CR2032-cell early 2000s redesigned Nut CPU with 3v fab process, manufactured in China
- 2-CR2032-cell 2015 ARM Cortex-M4, manufactured in the Philippines, firmware build date 2015-10-30, "C 2008 HP"

All three give the exact same behaviour with respect to the stack: One level of stack push. The initial value of T was dropped, initial value of Z pushed to T, initial value of Y pushed to Z, X to Y, and PV pushed to X.

And the 12CP in my possession (2-CR2032-cell, "Ver 02", "C 2004 HP") is the only one which exhibits the odd behaviour of intermixing the intermediate financial inputs onto the stack even though I didn't press ENTER.

Not at all surprising that the CP would be the only one that's different, considering that it is the only one that is known to be running unique firmware written from scratch for that machine (note, I don't have any specimens of the original Ver 1 12CP firmware written by Kinpo, only the Ver 2 12CP firmware which was created after HP's intervention.)